58 Keysight InfiniiVision HD3-Series Oscilloscopes User's Guide
3 Vertical Controls
1 Open the Channel dialog box by selecting the Channel badge or by choosing
Sources > Channel N... from the main menu.
2 In the Channel dialog box, select Coupling to select the input channel coupling:
• DC — DC coupling is useful for viewing waveforms as low as 0 Hz that do not
have large DC offsets.
• AC — AC coupling is useful for viewing waveforms with large DC offsets.
When AC coupling is chosen, you cannot select 50Ω mode. This is done to
prevent damage to the oscilloscope.
AC coupling places a 10 Hz high-pass filter in series with the input
waveform that removes any DC offset voltage from the waveform.
Note that Channel Coupling is independent of Trigger Coupling. To change trigger
coupling see "To select the trigger coupling" on page 155.
To specify channel input impedance
1 Open the Channel dialog box by selecting the Channel badge or by choosing
Sources > Channel N... from the main menu.
2 In the Channel dialog box, select the Impedance:
• 50 Ohm — matches 50 ohm cables commonly used in making high frequency
measurements, and 50 ohm active probes.
When 50 Ohm input impedance is selected, it is displayed with the channel
information on-screen.
When AC coupling is selected (see
"To specify channel coupling" on
page 57) or excessive voltage is applied to the input, the oscilloscope
automatically switches to 1M Ohm mode to prevent possible damage.
• 1M Ohm — is for use with many passive probes and for general-purpose
measurements. The higher impedance minimizes the loading effect of the
oscilloscope on the device under test.
If the channel is DC coupled, you can quickly measure the DC component of the signal by
simply noting its distance from the ground symbol.
If the channel is AC coupled, the DC component of the signal is removed, allowing you to use
greater sensitivity to display the AC component of the signal.
When you connect an AutoProbe, self-sensing probe, or a compatible InfiniiMax probe, the
oscilloscope automatically configures the analog input channels to the correct impedance.
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